The XBL test is being removed because it was the only remaining consumer of
xbl's implements="interfacename" in the tree, and was triggering QI on elements
for that codepath.
I've verified that a try run that MOZ_CRASHes when the C++ binding
QueryInterface implementation is invoked is green with these changes.
Differential Revision: https://phabricator.services.mozilla.com/D48249
--HG--
extra : moz-landing-system : lando
